For creating broadband antennas with low production costs, conventionally Vivaldi-antennas are used. Vivaldi-antennas consist of a tapered slotline antenna on a circuit board. Regular Vivaldi-antennas though create an electrically short antenna with a dipole-mode of radiation at signal frequencies where the antenna width W is approximately shorter than half of the signal wave length (W<λ/2). At those frequencies, unwanted radio frequency currents flow on the outer shield of the feeding coaxial cable. Thus, the cable provides unbalanced feeding and becomes an antenna part, too. This deforms the radiation pattern towards a dipole-like radiation pattern. For example, the European Patent EP 1 425 818 B1 shows such a Vivaldi-antenna. Furthermore the electrically short antenna provides typically poor reflection coefficient at the feeding port.
Accordingly, the object of the invention is to create a broadband antenna with a highly directive radiation pattern and low reflection coefficient.